A simple method to measure the twist elastic constant of a nematic liquid crystal

We demonstrate a simple method for measuring the twist elastic constant (K₂₂) of a nematic liquid crystal (LC). By adding some chiral dopant to an LC host, the LC directors rotate 180° in a homogeneous cell, which is known as 180° super-twisted nematic (STN) cell. By preparing two such STN cells with different chiral concentrations and measuring their Fréedericksz threshold voltages, we can obtain the K₂₂ and helical twisting power simultaneously. In the whole process, there is no need to measure the pitch length. Our obtained K₂₂ values agree well with those reported by using other methods.     

试论唐代的太子监国

太子监国是唐代政治中的重要现象,一般可分为太子攘夺皇权后的监国、皇帝巡幸时的太子监国、皇帝有疾诏令太子监国和权臣宦官废皇帝后以太子监国等类型。太子攘夺皇权和临危受命下的监国往往已掌握了国家的实际权力。有唐一代的太子监国现象不仅凸显了唐代统治集团内部的倾轧,也在一定程度上暴露了中国古代皇权传承中的制度纽结和实践困境。     

H桥多电平逆变器的新型调制

针对传统PD调制法应用在级联H桥多电平逆变器时存在的输出功率不均衡问题,提出一种基于1/4输出周期载波循环的优化调制策略,使得逆变器各级联单元的输出功率均衡,且开关管的最高开关频率降为原来的一半,降低了开关损耗.该优化调制策略比传统PD调制需要的三角载波数量更少,调制更简单.以四单元级联H桥多电平逆变器为例进行理论分析,并通过仿真实验验证了所提方法的正确性.     

ATM网络中基于控制理论的流量控制机制设计方法综述

未来的计算机网络将是一种能够提供多种不同服务 ,以支持多种不同应用需求 ,有着集成服务支持能力的高速分组交换网络 .为充分提高该类网络性能 ,设计一个高效的流量控制机制是一个关键问题 .为此 ,以ATM网络中的相关研究为背景 ,首次从控制理论的角度系统地分析和论述了高速网络中流量控制机制的组成并着重分析了其速率调节算法的设计 对目前已经提出的各种典型速率调节算法进行了对比分析 ,为进一步研究提出了新的课题和思路     

海带和裙带菜对鼠乳腺发育调控的研究

利用组织学技术研究海带（Laminaria japonica Aresch）和裙带菜(Undaria pinnatifida Harv.）在昆明系小鼠乳腺发育过程中的作用时发现，海带和裙带可明显提高鼠的受孕率，是对照组的2．5倍；刺激和加速乳腺上皮繁殖产生许多新的腺泡，这些腺泡的细胞在短时间内不断分裂，体积不断增大，细胞变为柱状或锥形，泡腔内储量有大量的乳汁。这种调节作用使乳腺快速进入授乳期。     

逆境型政府规制理论与食品安全危机防控

以德罗尔的逆境中的政策制定理论为基础，分析了“食品安全危机”治理中逆境型政府规制在伦理、模式、能力和自主性方面的缺失，提出了运用逆境型政府规制理论防控食品安全危机的对策：重视伦理道德建设；调整统计权的模式；调整事故调查的模式；完善规制责任追究制度；完善消费者损害赔尝制度。     

基于物联网技术的海上原油过驳智慧监管研究

分析了我国现存监管手段的不足，针对实际监管要求，基于信息化技术的快速发展及物联网技术在其他领域的成功应用，提出海上原油过驳的智慧监管体系的总体构架，并阐述了有关功能，为以后建设基于物联网技术的海上原油过驳智慧监管体系提供了参考。     

Phase-controlled all-optical switching based on coherent population oscillation in a two-level system

We theoretically propose a scheme of phase-controlled all-optical switching due to the effect of degenerate four-wave mixing (FWM) and coherent population oscillation (CPO) in a two-level system driven by a strong coupling field and two weak symmetrically detuned fields. The results show that the phase of the FWM field can be utilized to switch between constructive and destructive interference, which can lead to the transmission or attenuation of the probe field and thus switch the field on or off. We also find the intensity of the coupling field and the propagation distance have great influence on the performance of the switching. In our scheme, due to the quick response in semiconductor systems, a fast all-optical switching can be realized at low light level.     

Reducing Power Consumption in Core Wavelength Division Multiplexing Optical Networks

Abstract

This work proposes some heuristic criteria aiming at saving energy by efficiently switching off optical fibers in generalized multi-protocol label switching-controlled optical networks during low traffic load periods and by taking into account network equipment power consumption. Simulations show that up to 80% of energy can be saved when the traffic is reduced by 20% with respect to its maximum. The impact of network design parameters is also investigated.